Generally, it is considered that an aqueous patch is not suitable to be applied for a long time relative to an oily patch. One of the reasons is the difficulty of controlling the water evaporation in an aqueous patch.
A moisture permeability of an aqueous patch is highly correlated with the properties of a backing. For example, when a woven fabric or a nonwoven fabric is used as a backing, the problem is that its high moisture permeability causes a decrease of the water content in the pasty preparation in a short time and hardens the pasty preparation, resulting in a decrease of the adhesive power. Meanwhile, when a film such as plastic is used as a backing, it can significantly block the water evaporation. However, when it is applied for a long time, a cohesive failure of the pasty preparation often occurs due to sweat, exudate from an affected area or the like, resulting in a decrease of adhesiveness of the patch, a rash caused by dampness and the like.
As a mean to solve the above-mentioned problems, an aqueous patch, which uses a backing having a two-layer structure consisting of a moisture permeable film and a fiber wherein the air permeability of the backing is adjusted, is proposed (Patent Documents 1-3).
However, during the storage of said aqueous patch, a component contained in the pasty preparation such as a fat permeates the film resulting in defects such as a wrinkle, a kink and the like, or the component exudes into the film surface resulting in problems such as stickiness.
Also, regarding a backing prepared by laminating a film and a nonwoven fabric or a woven fabric, an attempt to control the moisture has been made by forming through-holes in the film (Patent Documents 4-5). However, in said backing, a sufficient control of the moisture permeability may not be achieved in some cases depending on the physical properties of the pasty preparation. Namely, a hard pasty preparation containing a fewer amount of liquid components does not sufficiently exude into the woven fabric or the nonwoven fabric, and thus the advantage of the through-holes in the film can not be utilized in some cases. Conversely, when a soft pasty preparation containing a more amount of liquid components is used, the pasty preparation or a liquid component exudes from the woven fabric or the nonwoven fabric and the moisture permeability become out of control, and further, the exudate from the through-holes may cause troubles such as stickiness.